If Robert was capable of surviving inside of the Room of Requirement because the Room provided him with the energy and sustenance he needed then wouldn't it be possible for him to have lived through this encounter if instead of leaving right away, the others had brought him actual food and water for a few days, at least one, before they let him leave the Room? Maybe that wouldn't be possible for Robert since nobody knew about it until three years after the fact but removing the Room's ability to sustain life for as long as the person is inside it seems like a bad idea, you could last a siege in it and have someone bring you food and water afterwards.
Also, people are capable of living longer than three or four days without food. Some people can survive over two months without food so long as they keep hydrated, depending on how healthy they are before they stop eating. If Robert were to die of anything from his four day stint in the Room of Requirement, it would be from the water he had consumed while in the Room suddenly leaving his body, not the energy draining from his mitochondria or the nutrients abandoning his flesh.
How could they alter the Room to align with Gamp's Great Exception, if Gamp hasn't even been born yet? Gamp was born three years after the fact and I highly doubt he went on to create the famous Law of Elemental Transfiguration as soon as he was born, which means people where altering extremely powerful magic to follow a concept several years before it was even conceived of, let alone published for all to see.

It is fact that humans survive more than 2 weeks without food. 3 days without water, but then water can be conjured. Aguamenti can conjure water from water vapor. Terry could have asked for a passage out, if he were smart enough.

Nevertheless, the story was brilliant. Well-researched. Believable. Imaginative. Great use of Potterverse and Its principles. Well, great writing, overall. The ending sentence, very apt. Love stories like this.

I'm happy you get to live your dreams, and I'm happy that you're sharing your talent. Thank you. :)